Folliculogenesis in vertebrates involves the developmental progression from a small primordial follicleto a large preovulatory follicle containing a fully competent oocyte arrested at the second meiotic metaphase by the time of ovulation. This entire process is regulated and coordinated by endocrine hormones such as the pituitary gonadotropins, and locally modulated by steroids and factors (inhibin/activin) acting in an autocrine/paracrine manner. The molecular nature of these factors is only now being elucidated. Gonadal peptides such as inhibin and activin are currently being recognized not only as regulators of the pituitary gonadotropins secretion, but also as multifunctional modulators in the ovary and in the utero-placental unit. In addition to their normal reproductive roles, inhibins and activins have been implicated in gonadal oncogenesis and pathologies of the reproductive system. In this regard, high levels of inhibin B are associated with granulosa cell carcinoma, and high levels of inhibin A are correlated with pre-eclampsia and Down syndrome during pregnancy. The understanding of the relationship of several gonadal peptides to the signals for gonadal function still has many unanswered questions. This proposal is designed to elucidate the molecular mechanisms underlying the expression and the paracrine and autocrine biological activities of inhibin/activin A and B. Although the different inhibin/activin isoforms (A and B) appear to have similar effects in the pituitary, there is also precedent suggesting that they may have distinct physiological roles in different tissues. The availability of recombinant inhibin/activin A and B now gives the possibility to assess the functions of the various inhibin/activin isoforms. In order to implement the above objectives, the following projects will be carried out:: a) Isolation and cloning of the inhibin/activin subunits (alpha,betaA,and betaB) from ovarian tissue, b) Antibodies against the inhibin/activin subunits will be generated to carry out western blot analysis, c) Expression of inhibin/activin subunits during follicle development and during the process of gonadotropic stimulation of oocyte maturation, d) Paracrine (local effect at neighboring cells) and autocrine (local effect in the same cells) biological activities (on steroidogenesis and oocyte maturation) of inhibin/activin A and B will be assessed using in vitro ovarian follicle cultures, to test the hypothesis that the various forms of the gonadal peptides may have distinct physiological roles in the ovary. The proposed research will furnish critically needed information about the molecular dynamics and actions of the inhibin/activin in the ovary. Understanding the physiology of inhibins and activins and the interplay of major endocrine and paracrine mechanisms involved in the ovary is essential to decipher the process of gonadal differentiation in both normal and disease conditions, and may ultimately help in the diagnosis and treatment of reproductive dysfunction in humans.